A.R. McLauchlin1, O. Ghita1 and B. Tübke2 Detection of Contaminants in Recycled Poly(ethylene terephthalate) (PET) by Near Infrared Spectroscopy A.R. McLauchlin1, O. Ghita1 and B. Tübke2 1College of Engineering, Mathematics and Physical Sciences, University of Exeter, UK 2Institute for Chemical Technology, Fraunhofer Institute, Karlsruhe, Germany

Contents Introduction: The SupercleanQ Project Materials and Methods Results Conclusions

SupercleanQ Aim Role of spectroscopy A post-market challenge test for validation of recycled food contact materials with 100% reliability rPET must comply with EC 282/2008 Role of spectroscopy Offline measurement of contaminants in rPET Inline measurement of degradable contaminants in rPET during injection moulding

Contaminants: Examples Limonene Fruit Juice Carbonated Beverages Acetaldehyde By-product of PET synthesis Benzophenone UV stabiliser

Concerns Over Purity of rPET If compounds can diffuse into PET, can they diffuse out again? Franz, R., Mauer, A., & Welle, F. (2004). Food additives and contaminants, 21(3), 265–286. Cecchi, T., Passamonti, P., & Cecchi, P. (2009). Is It Advisable to Store Olive Oil in PET Bottles? Food Reviews International, 25(4), 271–283.

Hansen Solubility Parameter Surrogate Mol. Wt g/mole B.Pt °C Dipole Moment D Hansen Solubility Parameter ACETALDEHYDE 44.05 20.2 2.7 20.9 BENZOPHENONE 182.22 305.4 2.98 22.1 PET   21.6 Sum of dispersive, polar and hydrogen bonding properties of a molecule Predictor of miscibility of two molecules Acetaldehyde and benzophenone likely to be absorbed by PET

Current Methods Thermal desorption / Solvent extraction Gas or Liquid Chromatography + MD* For: Sensitive, accurate Against: Slow, expensive Need for rapid, sensitive method *Franz, Mauer & Welle (2004)

Materials and Methods Previous work: “Single Dose” Aim: To achieve a range of concentrations Volatility (b.pt. Acetaldehyde = 20°C) Precludes melt compounding Chosen approach: Uptake from aqueous solutions of various concentrations

Impregnation Pristine juice bottles Acetaldehyde or Benzophenone 2mg/l - 400mg/l 10% Methanol in all Benzophenone solutions 5 days @ 50°C + 20 days @ 20°C in the dark

Analysis Bottle wall only was sampled PET analysis: Water analysis: Benzophenone: TD-GC-MS Acetaldehyde: TD + 2,4-DNPH then HPLC-DAD Water analysis: HPLC-DAD Acetaldehyde: 2,4-DNPH derivative Benzophenone: no derivatisation

Spectroscopy Apparatus 21 spectra / bottle Bruker Matrix Ocean Optics QP600 probes 21 spectra / bottle 16 scans 12000 - 4000cm-1 4cm-1 resolution

Data Analysis Predictive Models: Model Tested Acetaldehyde: OPUS 6.5 Quant2 Optimisation 15 out of 21 spectra used Outliers deselected Model Tested 5 additional spectra Not used in the validation Acetaldehyde: No spectral preprocessing Benzophenone Straight Line Subtraction

Data Analysis Spectral ranges: Both: 10000-7500cm-1 2nd and 3rd overtone C-H Benzophenone: 6100-4250cm-1 1st overtone CH CH2 CH3 Acetaldehyde: 4600-4250 cm-1 Aldehyde groups < 0.12AU

PET Analysis: Benzophenone Benzophenone detected in all but 2 treatments

PET Analysis: Acetaldehyde Acetaldehyde not detected in any sample Acetaldehyde + ethylene glycol = acetal product: 1-methyl-2,3-dioxolane

Validation Curve: Acetaldehyde RMSECV = 11.1 Initial rank = 9 Final rank = 6

Validation Curve: Benzophenone RMSECV = 13.6 Initial rank = 9 Final rank = 7

Factor Analysis 1 Maxima coincide with absorbance maxima for PET Spectral variation arises from interaction of analyte with PET. Factors 1+2+3= 95% of spectral variance

% of total variance represented by: Factor Analysis 2   % of total variance represented by: Analyte Factor 1 Factor 2 Factor 3 Factor 4 Factor 5 Total Acetaldehyde 87.5 6.8 0.8 0.5 0.4 95.9 Benzophenone 87.3 7.2 0.7 96.0 Factors 1 & 2 accounted for most of the variance

Factor Analysis 3: Score Plots Acetaldehyde Benzophenone

Testing the Model: Acetaldehyde Coefficient of 0.897: underestimates Acetaldehyde conc. Detection limit in PET could not be defined

Testing the Model: Benzophenone Coefficient of 1.0074: good correspondence Effective range 10-380 mg/kg PET

Conclusions NIR detected presence of acetaldehyde and benzophenone Linear PLS models obtained in both cases Good prediction of benzophenone Underestimate of acetaldehyde Response to acetaldehyde may have been due to reaction product with ethylene glycol

Acknowledgements The research leading to these results was performed as part of the SupercleanQ Project, funded by the European Union’s Seventh Framework Programme under grant agreement no. 285889 www.supercleanq.eu